A validated theoretical approach to predict the effect of ambient temperature and ethanol concentration on the event-averaged pMDI droplet size




The presence of ethanol in the formulation and decrease in ambient temperature, are known factors which are influential in pMDI mean droplet size increase and reduction of the fine particle dose. In this paper we introduce a two-stage theoretical approach to predict the relative influence of these factors on pMDI droplet size. In general, model predictions show a reduction in droplet size, as ethanol increases in the formulation. The magnitude of this reduction for 20°C and 35°C is predicted well by the model. For 45 °C, the model underpredicts the droplet size by around 50% which could be attributable to inaccuracies in mixture pressure values and/or inadequate representation of HFA/ethanol binary mixture transport properties such as viscosity and surface tension. Once sufficiently validated, this approach can reduce the need of numerous in-vitro trials.